In recent years, wind turbine generator systems utilizing wind power have been increasingly prevalent in view of conservation of global environment. The wind turbine generator system converts kinetic energy of a wind into rotary energy of a wind turbine rotor including wind turbine blades and a hub, and further coverts the rotary energy into electric power energy using a generator.
While the wind turbine generator system is in operation, the wind turbine rotor is subjected to an aerodynamic load from the wind. The length of each wind turbine blade has been increasing consistently with the growing size of the wind turbine generator system. This also increases aerodynamic loads acting on the wind turbine blades and thus a load imposed on each blade root portion.
As a method for suppressing the adverse effects of such an aerodynamic load, Patent Document 1 discloses a technique in which reinforcing ribs are arranged on an inside surface of the cylindrical blade root portion along a circumferential direction to reduce the deformation of the blade root portion, more specifically, to reduce the ovalization of the blade root portion.